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Alla [95]
3 years ago
8

Joe is 20 years old. His sister is half his age less 7. How old is his sister?

Mathematics
1 answer:
MakcuM [25]3 years ago
3 0
The answer is 3. 20/2=10 10-7=3
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The time for a visitor to read health instructions on a Web site is approximately normally distributed with a mean of 10 minutes
klio [65]

Answer:

a) The mean is 10 and the variance is 0.0625.

b) 0.6826 = 68.26% probability that the mean time of the visitors is within 15 seconds of 10 minutes.

c) 10.58 minutes.

Step-by-step explanation:

To solve this question, we need to understand the normal probability distribution and the central limit theorem.

Normal Probability Distribution

Problems of normal distributions can be solved using the z-score formula.

In a set with mean \mu and standard deviation \sigma, the z-score of a measure X is given by:

Z = \frac{X - \mu}{\sigma}

The Z-score measures how many standard deviations the measure is from the mean. After finding the Z-score, we look at the z-score table and find the p-value associated with this z-score. This p-value is the probability that the value of the measure is smaller than X, that is, the percentile of X. Subtracting 1 by the p-value, we get the probability that the value of the measure is greater than X.

Central Limit Theorem

The Central Limit Theorem establishes that, for a normally distributed random variable X, with mean \mu and standard deviation \sigma, the sampling distribution of the sample means with size n can be approximated to a normal distribution with mean \mu and standard deviation s = \frac{\sigma}{\sqrt{n}}.

For a skewed variable, the Central Limit Theorem can also be applied, as long as n is at least 30.

Normally distributed with a mean of 10 minutes and a standard deviation of 2 minutes.

This means that \mu = 10, \sigma = 2

Suppose 64 visitors independently view the site.

This means that n = 64,  = \frac{2}{\sqrt{64}} = 0.25

a. The expected value and the variance of the mean time of the visitors.

Using the Central Limit Theorem, mean of 10 and variance of (0.25)^2 = 0.0625.

b. The probability that the mean time of the visitors is within 15 seconds of 10 minutes.

15 seconds = 15/60 = 0.25 minutes, so between 9.75 and 10.25 seconds, which is the p-value of Z when X = 10.25 subtracted by the p-value of Z when X = 9.75.

X = 10.25

Z = \frac{X - \mu}{\sigma}

By the Central Limit Theorem

Z = \frac{X - \mu}{s}

Z = \frac{10.25 - 10}{0.25}

Z = 1

Z = 1 has a p-value of 0.8413.

X = 9.75

Z = \frac{X - \mu}{s}

Z = \frac{9.75 - 10}{0.25}

Z = -1

Z = -1 has a p-value of 0.1587.

0.8413 - 0.1587 = 0.6826.

0.6826 = 68.26% probability that the mean time of the visitors is within 15 seconds of 10 minutes.

c. The value exceeded by the mean time of the visitors with probability 0.01.

The 100 - 1 = 99th percentile, which is X when Z has a p-value of 0.99, so X when Z = 2.327.

Z = \frac{X - \mu}{s}

2.327 = \frac{X - 10}{0.25}

X - 10 = 2.327*0.25

X = 10.58

So 10.58 minutes.

6 0
2 years ago
A drilling machine can drill 12 holes in 6 minutes.If the machine drill holes at a constant speed, it can drill holes in 25 minu
Zielflug [23.3K]

Answer:

Did you mean to ask how many holes can the drill drill in 25 minutes, then the answer is 50

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2 years ago
Find the product of each polynomial (3a+5b)​
serg [7]
Roaa s Bono de hehdowbdd
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3 years ago
AB=4x+3 and CD=24+5x find bc
madam [21]

Answer:

Step-by-step explanation:

1. use distribution factor

(4x+3)(24+5x)

4x times 24 = 96

4x times 5x = 20x

3 times 24 = 72

3 times 5x = 15x

2. combine like terms

96 + 72 = 168

15x + 20x = 35x

35x + 168 or 168 + 35x

I may be wrong please check my answer. I may have a lapse in my algebra, or I may have misunderstood the problem. But this is what I can give you to the best of my knowledge.

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3 years ago
Which of the following would be a good reason to place your money into a savings account?
tatyana61 [14]

Answer:

B

Step-by-step explanation:

you are not supposed to withdrawal money from a savings account

5 0
2 years ago
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